Chrome-nickel hardenable stainless steel



States Patet Ofifice 2,695,229 Patented Nov. 23, 1954 Claude M. Sheridanand William C. Benzer, New Kensington, Pa., assignors to Alle hcnyLudlum Steel Corporation, Brackenridge, Pa., a corporation ofPennsylvania No Drawing. Application October 28, 1950,

Serial No. 192,830

2 Claims. (Cl. 75128) This invention relates to a new and improvedstainless steel alloy of a martensitic type basically having a superiorcorrosion resistance and also having highly 1mproved mechanicalproperties at elevated temperatures.

One characteristic of our alloy is its hardness, creep strength andstability under high temperatures and high temperature utilizations. Itssuperior corrosion resistance makes it important in the cutlery field.Its high temperature mechanical properties are important from thestandpoint of the conditioning and shaping of cutlery and particularly,from the standpoint of high temperature utilizations of a product madefrom the alloy. In the latter connection, it is suitable for use inconnection with engine valves, steam turbines, etc.

Although ferrous chromium stainless steels have been before used in themanufacture of blades for cutlery, they have had a limited acceptance byreason of their tendency to pit and corrode after a period of use due tocontact with contaminating agents, such as mineral acids, copper andferric chlorides, etc. The present alloy not only provides a requisitemirror finish for such a utilization, but has a much superior life-timeresistance to pitting and corroding, such that it is suitable forhighest quality cutlery.

It has been an object of our invention to provide a new and improvedalloy of the described type that has essentially a highly superior roomtemperature corrosion resistance from a long-term standpoint;

Another object has been to provide a chromium-nickel alloy of thedescribed type which will also have highly improved mechanicalproperties at elevated temperatures.

In carrying out our invention, we have determined that the carboncontent is highly critical and should be below a maximum of about .10%(optimum of .08% or lower). We have determined that hardness can beobtained with this low carbon content, provided the essential elementschromium, nickel, molybdenum, silicon and manganese are within thecertain specified ranges or maximums as the case may be. Prior to thepresent invention, a higher carbon content was necessary to providerequisite harden-ability. We have found that carbon above the maximumspecified is deleterious from the standpoint of a lowering of corrosionresistance and additionally, that the desired hardenability can beobtained by properly proportioning the other essential elements andparticularly, by proportioning them with respect to the nickel content.A characteristic of our alloy is that it will harden to a minimum of 35Rockwell C.

The alloy of our invention fills a definite need in the art for asuperior cutlery steel of a stainless type and it can be provided with alife-time bright finish that is highly resistant to corrosion. Inaddition, it is highly suitable for valve and turbine utilizations wherestability and creep strength as well as hardness and corrosionresistance are needed.

The alloy of our invention contains the following elements in theproportions stated:

max. (optimum about .08% (optimum 10 to 15%) max.)

In this alloy, critical based on the molybdenum content, the nickelcontent is critical tent, and the maximum carbon content is highlycritical. An optimum alloy, especially from the standpoint of corrosionresistance has the following content:

C=.08% max.

Cr= 12 to 15% Ni=2 to 3.5%

Mo=2.5 to 3.5%

Si=.50% max.

Mn=.50% max.

Remainder substantially all iron with incidental impurities.

Alloy Type g gf iz ggb gf Ferric Chloride 431 2 3 Pits badly. Ours 001025 Little or no pitting.

The alloy of (b) is highly suitable for cutlery usage, while the alloy(a) is suitable for both cutlery and high temperature utilizations.

What we claim is:

1. A highly superior stainless steel alloy of a martensitic type that ischaracterized by its exceptionally high room temperature resistance tocorrosion and pitting on a long-term basis from both the standpoint ofacid and copper chloride and ferric chloride attack,"by its ability tobe hardened to a minimum of about 35 Rockwell C, and by its improvedmechanical properties at elevated temperatures and which, with iron andincidental impurities, contains as its essential elements carbon,chromium, nickel and molybdenum in a critically proportioned andbalanced relationship; the alloying elements consisting of a highlycritical maximum carbon content of below .l0%, about 10 to 17% chromium,about 1 to 4% nickel, about 1 to 4% molybdenum, and up to a maximum ofabout .50%, each of silicon and manganese.

2. A highly superior stainless steel alloy of a martensitic type forhigh temperature and essentially for high quality cutlery usage that ischaracterized by its high room temperature resistance to corrosion andpitting on a long-term basis from both the standpoint of acid and copperchloride and ferric chloride attack, by its ability to be hardened to aminimum of about 35 Rockwell C, and by its improved mechanicalproperties at elevated temperatures and which, with iron and incidentalimpurities, contains as its essential elements carbon, chromium, nickeland molybdenum in a critically proportioned and balanced relationship;the alloying elements consisting of below .08% carbon, about 12 to 15%chromium, about 2 to 3.5% nickel, about 2.5 to 3.5% molybdenum, and upto a maximum of .50%, each of silicon and manganese.

References Cited in the file of this patent London, England.

the ranges of chromium and nickel are r from the standpoint of thecarbon con-

1. A HIGHLY SUPERIOR STAINLESS STEEL ALLOY OF A MARTENSITIC TYPE THAT ISCHARACTERIZED BY ITS EXCEPTIONALLY HIGH ROOM TEMPERATURE RESISTANCE TOCORROSION AND PITTING ON A LONG-TERM BASIS FROM BOTH THE STANDPOINT OFADIC AND COPPER CHLORIDE AND FRRIC CHLORIDE ATTACK, BY ITS ABILITY TO BEHARDENED TO A MINIMUM OF ABOUT 35 ROCKWELL C, AND BY ITS IMPROVEDMECHANICAL PROPERTIES AT ELEVATED TEMPERTURES AND WHICH, WITH IRON ANDINCIDENTAL IMPURITIES, CONTAINS AS ITS ESSENTIAL ELEMENTS CARBON,CHROMIUM, NICKEL AND MOLYBDENUM IN A CRITICALLY PROPORTIONED ANDBALANCED RELATIONSHIP; THE ALLOYING ELEMENTS CONSISTING OF A HIGLYCRITICAL MAXIMUM CARBON CONTENT OF BELOW .10%, ABOUT 10 TO 17% CHROMIUM,ABOUT 1 TO 4% NICKEL, ABOUT 1 TO 4% MOLYBDENUM, AND UP TO A MAXIMUM OFABOUT .50%, EACH OF SILICON AND MANGANESE.